Liquid crystal display devices can be driven with a battery for several hours due to their low power consumption. The occupied space is narrow due to a small volume, and it is portable due to a light weight. For these reasons, the liquid crystal display devices have been used in various applications. In addition, the sizes of a product may vary from small-sized to large-sized. The display devices trend to use a mobile phone as the small-sized and a large TV as the large-sized. In particular, in the case of the medium and large-sized liquid crystal display devices, having clear image quality at a light viewing angle of the wide angle and enhancing the brightness contrast at ON/OFF of the drive cells are important to ensure the display quality.
The liquid crystal display devices have been used or developed as various liquid crystal modes such as dual domain TN, ASM (axially symmetric aligned microcell), VA (vertical alignment), SE (surrounding electrode), PVA (patterned VA) and IPS (in-plane switching) mode. Each of these modes has a unique liquid crystal alignment and a unique optical anisotropy. Therefore, due to the optical anisotropy of these liquid crystal modes, compensation films with various optical anisotropy are required to compensate changes in the optical axes of the linearly polarized light.
For the compensation films, it is important to have the optical anisotropy not only for the optical compensation due to the liquid crystal which is an optically anisotropic substance but also for the improvement of the light leakage occurring at a light viewing angle of around 45° from the optical axis of the orthogonal polarization elements.
Therefore, for the optical compensation of the liquid display of various modes, the development of the optical film capable of controlling the optical anisotropy precisely and effectively is as importance as anything else.
Further, in the case of the optical film which is used for display devices with more than 30 inch-large screen, it needs to be stretched to a high stretching ratio. The optical film is produced by stretching a polymer film under high-temperature and high-humidity, and it is highly likely that dimensional changes may occur in this process. If the dimension of the polymer film is changed, a stress is generated between the polarizing element and the resin film. When the screen displayed black, it is likely to cause a corner unevenness in which corner portion is missing in white color. Therefore, in order to produce an optical film which is suitable for a large screen, polymeric materials with small dimensional changes are required even in the case where it is stretched to a high stretching ratio.
Meanwhile, homopolymers or copolymers of cyclic olefins are well known through literatures or the like. The cyclic olefin-based polymers produced by addition polymerization using a homogeneous catalyst have a cyclic structure which is hard and sterically bulky to monomeric units of all the main chain. Thus, these polymers are amorphous polymers having very high glass transition temperature (Tg), and there is no light loss due to scattering as in crystalline polymers. Furthermore, there is no light absorption in the visible ray region due to the p-conjugation. In particular, the cyclic olefin-based polymers having a relatively large molecular weight which are produced by addition polymerization using an organic metal compound as a catalyst have a low dielectric constant and an electrically excellent isotropy.
Due to such physical properties such as a high permeability, a low double refractive index and a high glass transition temperature (Tg), the polymers polymerized using norbornene monomers can be used for optical application such as a light-guiding plate or an optical disc. They can also be used as an insulating material due to their low dielectric constant, excellent adhesion strength, electrical isotropy and high glass transition temperature (Tg).
However, since the optical films produced by polymers or copolymers of conventionally known cyclic olefins have a very high retardation value in the thickness direction, there is a need to develop a method capable of controlling this retardation value properly.
Given the above circumstances, the present inventors have conducted extensive studies to develop a composition for an optical film capable of having excellent optical properties as well as controlling the retardation value in the thickness direction of the optical film. As a result, the inventors found that the composition for an optical film comprising silicone resins as described below satisfies the above requirements, and completed the present invention.